1. Field of the Invention
This invention relates to a dispensing device, in particular a device where the active fluid is oxygen or nitrogen gas which has been released from a solid state electrochemical cell, and where the pressure increase resulting from the release of such gas pushes fluid from a bladder within a pressure-tight chamber through an outlet in a steady continuous flow until the fluid contents of the bladder are exhausted.
2. State of the Art
Richter in U.S. Pat. No. 3,894,538 disclosed a device for dispensing medicines to man or beast. The medicine was contained in a flexible container which became compressed as fluid was electro-osmotically or electrolytically introduced into an adjacent flexible chamber. The rate of medicine discharge was regulated by using a potentiometer.
Maget in U.S. Pat. No. 4,522,698 disclosed electrochemical prime movers. Embodiments of the invention include a device for dispensing pharmaceuticals to a human body over a substantial period of time at a sustained very low rate, where a battery provides the driving force to transport an electrochemically active gas from a precharged chamber to a second chamber through an ion-exchange membrane. Oxygen from air was disclosed as moving across an ion-exchange membrane to pressurize a chamber. Pressure in a chamber increases as electroactive gas transports across the membrane, this increase in pressure drives a piston which forces the contained pharmaceutical fluid to flow through an outlet. The invention requires electrodes which are electrically conductive and act as catalyst to convert molecules to ions; titanium-palladium alloy or palladium black are recommended materials. A controller is utilized to control the magnitude and time pattern of current and voltage applied to the membrane as well as to turn current on and off. To function, the invention requires either exposure to air or precharging with an electroactive gas.
Maget in U.S. Pat. No. 4,886,514 disclosed electrochemically driven drug dispensers. A potential from an external power source drives an electrochemically active gas such as hydrogen or oxygen to be transported across a membrane from a fixed volume chamber to a chamber which has a variable volume. The volume of the chamber varies by either flexing am expansible diaphragm type wall or by displacing a sliding wall, said wall is shared by a second variable volume chamber which contains a fluid drug to be administered. As the electrochemically active gas is transported to the first variable volume chamber, the drug is forced out of the second variable volume chamber through an outlet. Countering the electrochemical transport of gas across the membrane, the gas diffuses in the opposite direction across the membrane in accordance to the pressure gradient and diffusivity properties of the membrane. A controller compensates for the gas diffusion rate and varies the voltage and current to achieve the desired drug delivery rate in a steady or intermittent mode. To function, the invention requires precharging with an electroactive gas.
Maget et al. in U.S. Pat. No. 4,902,278 disclosed a fluid delivery micropump. The pump utilizes an air-actuated battery in a fixed closed circuit with an electrochemical cell which drives the transport of oxygen in air across a membrane. The transport applies external pressure to a collapsible reservoir filled with fluid, as a result, fluid is expelled from the reservoir through an outlet. The membrane is preferably a Nation material (a perfluoro sulfonic polymer) which has been coated with platinum black/10% Teflon. Electrodes are preferably titanium screens. To control the current, a resistor is utilized. The device is activated by removing a protective peel tab to expose air inlet ports to the battery cathode. A disadvantage of this type of system is that shelf life of the device is dependent on the integrity of the seals which prevent air leakage to the battery. If the seals are not perfect, the battery will slowly discharge before the desired time of use. To function, the invention requires exposure to air.
The prior art includes several devices which are capable of performing the general function of the device presently disclosed; however, the prior art has not satisfied a demand which exists for a device which 1) has a design which can dispense a fluid over a nearly constant rate for an extended period of time, 2) has a simple design which is conducive to fabrication, 3) does not require exposure to air, fluid or the precharging of an electrochemically active gas to function, 4) does not utilize polymeric ion-exchange membranes which typically must remain hydrated to some degree to function and which are affected by humidity, which can cause changes in conductivity, gas flow and dispensing rates.